Cements in clinical dentistry

• Restorative materials.
The cements must have adequate resistance to dissolution in the oral environment.It must also develop an adequately strong bond through mechanical interlocking and adhesion, good bonding to enamel and dentin, low toxity.High strength in tension, shear, and compression is required, as is good fracture toughness to resist stresses at the restoration-tooth interface.Good manipulation properties, such as adequate working and setting times, are essential for successful use.The materials must be biologically aceptable.
Most cements are powder-liquid materials.Some recent materials are composed of two pastes.Cements set by chemical reaction between the ingredients(often an acide-base reaction) or involve polymerization of a monomeric components.
b) eugenol-free (noneugenol) cements;
c) resine cements.
2. Permanent cements;
Classification of dental cements according to bonding mechanism:
1.Phosphate: a) zinc phosphate;
b)zinc silicophosphate;
2.Phenolate: a) calcium hydroxide silicylate;
b) ZnO eugenol: -polymer;
-EBA;
-alumina;
3.Polycarboxylate:a) zinc polycarboxylate;
b) glass ionomer;
4.Resin: a)poly(metylmetacrylate);Glass ionomer + polymetelmetacrylate=Hybrid ionomers.
b) dimethylacrylate: -filled;
-unfilled.
Bonding mechanizm
Nonadhesive luting The luting agent served primarily to fill the gap and prevent entrance of fluids.Zinc phisphate cement, for example, exibits no adhesion on the molecular level.It holds the restoration in place by engaging small irregularities on the surfaces of both tooth and restoration.The nearly parellel opposing walls of a correctly prepared tooth without shearing or crushing the minute projections of cement extending into reccesses in the surface.
Micromechanical bonding.Resine cements have tensile strenhtgs in the range of 30-40MPa, which is aproximately five times that of zinc phosphate cements.When used on pitted surfaces, they can provide effective micromechanical bonding.The tensile strength of such bonds can sometimes exceed the cohesive strength of enamel.This allows the use of less extensive tooth prepararion for restorations such as ceramic veneers and resin-bonded fixed partial dentures.The deep irregularities necessary for micromechanical bonding can be producted on enamel surface by etching with phosphoric acid solution or gel;on ceramic by etching with hydrofluoric acid, and on metals by electrolytic etching, chemical...

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